Construction for cooling a continuously cast string

ABSTRACT

Continuously cast strings are cooled, first by spraying of water, and secondly by means of cooling rolls providing conditions for heat transfer quantitatively decreasing from the center towards the ends in axial direction, of an individual roll.

United States Patent Scheufele [4 1 Feb. 15,1972

[54] CONSTRUCTION FOR COOLING A CONTINUOUSLY CAST STRING 72] Inventor: Erwin Scheufele, Duisburg-Ungelsheim,

Germany [73] Assignee: Kabel-und Metallwer'ke Gutehoffnungshutte Aktiengesellschaft, Vahrenwalder Strasse, Germany [22] Filed: Feb. 9, 1970 [21] Appl. No.: 9,523

[52] US. Cl ..164/283, 164/82 [51] Int. Cl ..B22d 11/12 [58] Field of Search ..164/82, 89, 282, 283

[56] References Cited UNITED STATES PATENTS 2,284,503 5/1942 Williams "164/ 282 'V .e66.ooo

3,399,716 9/1968 ROSSI et al 164/89 3,433,289 3/1969 Schrewe ..164/282 3,536,127 10/1970 Tafel ..l64/283 FOREIGN PATENTS OR APPLICATIONS 1,399,695 4/1965 France.... .....164/282 1,105,567 4/1961 Germany ..164/283 932,196 7/1963 Great Britain Primary ExaminerR. Spencer Annear Att0rney--Smyth, Roston & Pavitt [57] ABSTRACT Continuously cast strings are cooled, first by spraying of water, and secondly by means of cooling rolls providing conditions for heat transfer quantitatively decreasing from the center towards the ends in axial direction, of an individual roll.

7 Claims, 4 Drawing Figures .OOOOOO ODOOOOO PAIENTEBFEB 15 m2 3.642.057

sum 1 or 2 In vent or Jaw/v rev aura;

CONSTRUCTION FOR COOLING A CONTINUOUSLY CAST STRING The invention relates to improvements of structure for cooling a casting string or slab having elongated rectangular cross section and having been produced by continuous casting. The invention is directed to particular rolls arranged in a guiding frame of the continuous casting machine, between a spray water zone therein and the last one of the driven rolls pertaining to the extruding and withdrawal device for the casting. The particular rolls are separated from the spray water zone by a device for removing spray water from the string, which removal device may particularly be comprised of a smooth roll engaging the string over its entire width on a continuous basis.

It is known to cool the casting string leaving a continuous casting mold by means of spray water. The spraying of water upon the hot surface of the string for cooling thereof offers the advantage that large quantities of heat can be removed in a short period of time. On the other hand, the spray water technique has the disadvantage that a vapor layer is formed cally on the hot surface of the string, and the locally variable distribution of the vapor layer produces nonuniform conditions for cooling.

In U.S. Pat. No. 2,284,503, corresponding to the German printed application No. 1,220,972, it has been suggested to eliminate cooling by means of spraying water, and to use instead cooling by means of cooled plates or rolls. This type of cooling operates less abruptly. Aside from functioning as cooling devices, these plates or rolls have the additional task of supporting the casting string so as to prevent bulging of the solidified shell of the string, the interior of the casting still being liquid at that point. The plates have to engage the flat casting string over the entire width thereof, and an adjustment of the cooling effect in relation to the entire string width is, therefore, not provided by these known cooling plates or rolls.

The invention solves the problem of obtaining proper cooling of a solidifying casting string so that the formation of cracks in the string due to nonuniform temperature reduction is being avoided, particularly upon cooling of casting strings such as continuous slabs, having elongated rectangular cross section. The cooling device in accordance with the invention uses means for spraying water onto the string as a first cooling stage, but supplementary cooling is provided in combination therewith. Rolls are provided for additionally cooling the same casting string behind the spray water zone. These cooling rolls are arranged in the frame containing the guiding equipment in a continuous casting machine, and they are located particularly between the spray water zone and the last one of the driven rolls. Moreover, as stated above, the cooling rolls are separated from a device, included in the guiding arrangement, for removing spray water from the string. Such a water removal device may particularly be constituted by a smooth roll engaging the string over its entire width. It is a particular feature of the invention, that these rolls, which may be cooled in their interior, do exert a cooling effect upon the central portion of the broad sides of the string with rectangular cross section, larger than cooling provided upon the string near the edges thereof.

Therefore, in accordance with the invention there is a combined cooling including a first, direct cooling (through spray water) and a second, indirect cooling (through rolls), the latter cooling being particularly adjustable at a higher degree of accuracy. The indirect cooling through rolls is thus adjusted so that a uniform temperature of the surface of the string is obtained, over the entire width thereof and including its edges. This provision, in turn, avoids formation of cracks in the slab casting as they may arise due to thermally induced internal tension.

The cooling rolls may be provided with internal cooling channels which are appropriately cooled. These channels as extending in the rolls are characterized particularly by an increase in distance from the cylindrical circumference of the rolls in relation to or as a function of distance from the center of the roll in axial direction towards the ends thereof. In accordance with another feature of the invention, the rolls can be provided with grooves near their ends. This in turn results in a reduction of the surface, on a per unit area basis, available for direct engagement by the roll of the casting string and for heat transfer. Accordingly the cooling effect provided by the rolls near the edges of the string is reduced as compared with more central regions thereof. In other words the conditions for heat transfer between casting string and cooling rolls are particularly relatively enhanced in (axial) central surface regions of the cooling rolls as compared with the conditions for heat transfer between axial end portions of the rolls and surface areas of the flat casting near its edges.

In accordance with another feature of the invention, the cooling effect can be reduced near the edges of the string or slab in that the cylindrical wall or wall surface of a cooling roll is provided with material of lower thermal conductivity near its axial ends than in its central portions. Therefore, the string engages, with its edge-near surface portions, cooling roll surfaces to which heat transfer is somewhat impeded as compared with heat transfer in central surface regions of the roll. One can obtain such a roll by providing tubular pieces made of rather poorly thermally conductive material and disposing these tubular pieces upon the axial ends of a roll. Alternatively, a layer of metal or oxide ceramic can be firmly deposited upon the rolls surface using, for example, the plasma spray method.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention, and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 illustrates somewhat schematically a side elevation of a continuous casting machine;

FIG. 2 illustrates in an enlarged scale a top elevation of a portion of the device shown in FIG. 1 whereby some of the rolls have been eliminated but solely for purposes of facilitating orientation and FIGS. 3 and 4 illustrate representative examples of cooling rolls.

Proceeding now to the detailed description of the drawings there is illustrated a continuous casting mold l for casting a string 2 with slab ingot type cross section, leaving the mold as a continuous string. By means of transportation rolls 9, the string is guided through two different cooling zones on its extraction and withdrawal path, for example, for veering into the horizontal. There is a first cooling zone which can also be described as a spray water zone and which is established by means of nozzles 5 arranged directly underneath mold 1 along the path of the casting string. Nozzles S are connected to a pipeline 4 for supplying water thereto. Thus, cooling water is sprayed directly upon the hot string 2 by means of these nozzles 5. The interior of string 2 is, of course, still liquidous as it enters the cooling zones. The transportation path includes and is defined in this cooling zone by rolls 3, and it can be seen that nozzles 5 are arranged to spray the cooling water in between adjacent ones of rolls 3.

As string 2 leaves the first cooling zone as defined by the nozzles 5, it passes a pair of rolls 6 having smooth surface and being disposed on opposite flat sides of string 2. These rolls engage string 2, over its entire width, and on both flat sides thereof to strip off spray water as it may still run thereon. This stripping off process is of decisive importance for the cooling effect provided by andin the second cooling zone.

The second cooling zone is established by means of rolls 7 which are cooled in their interior. However, these rolls are not necessarily provided with particular coolants in their interior as long as a sufficiently large temperature differential can be maintained. In this second cooling zone heat is removed from the string, through direct engagement with rolls 7. In order to avoid a nonuniform temperature reduction of the string across the width thereof as corresponding to the long side of the rectangular. cross section, rolls 7 are particularly constructed;

As stated above, for example, and as shown in FIGS. 3 and 4 the rolls may be provided in their interior with cooling channels 11. In FIG. 3 the cooling channels may have particularly selected distance from the cylindrical circumference of a roll in radial direction therein. This radial distance varies in axial direction in the cylindrical roll to be smaller in the central roll portion than near the axial ends thereof. In addition or in lieu thereof rolls 7 may be provided with grooves 8 near their ends, as shown in FIG. 2, so as to reduce, on a per unit area basis, the surface available for contact between rolls 7' and string 2. In either case, the respective central portions of the broad surfaces of string 2 as engaging cooling rolls 6, are subjected to stronger cooling than the surface portions near the edges thereof. This in effect operates as temperature equalization in the solidified shell portion of the string.

In the alternative, but for the same purpose, the cylinder wall near the axial end of a roll 6 as provided to engage zones of the string 2 near its edges, may be made from a material that impedes, relatively speaking, heat transfer between string and roll. This is shown in FIG. 4. The heat transfer between string and cooling roll is, relatively speaking, enhanced. Rolls for such axially variable heat transfer may be provided near the edges with a sprayed-on metallic or oxide ceramic layer such as 10 of roll 7.

The invention can be practiced in, continuous casting machines wherein the continuous cast string is veered into the horizontal, but the invention can also be used for vertically operating machines. In cases the continuously cast string is bent and reoriented, cracks and fissures may occur particularly near the edges if the temperature of the string near its edges is too low as a result of strong overall cooling, so that there is nonuniform temperature reduction setting up thermal stress in the string. The nonuniform, axially variable heat transfer conditions established by rolls made in accordance with the teaching of this invention provides uniform thermal conditions and uniform temperature reduction of the string across its width.

2 he invention is not limited to the embodiments described above, but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be covered by the following claims.

I claim:

1. Arrangement for cooling a continuous casting string having elongated rectangular cross section and being guided within a particular guiding frame underneath a casting mold, the combination comprising:

first means arranged directly underneath the casting mold to establish a spray water zone for cooling the string by spraying water upon its surface;

second means disposed behind the spray water zone in direction of the casting withdrawal path to remove spray water from the casting string;

and third means including a plurality of rolls in contact with the broad sides of the string arranged behind the second means in direction of casting withdrawal, said rolls including heat transfer means for extracting more heat from the axial center of the rolls than from the ends.

2. Arrangement as in claim 1, the second means including at least one roll having smooth walls engaging the casting string over its entire width.

3. The arrangement as in claim 1, the rollsincluded in the third means being internally cooled and having internal cooling channels, the radial distance of the channels from the cylindrical surface of the roll being larger at the axial cylinder ends than near the central portion of the rolls.

4. The arrangement as in claim 1, the rolls included in the third means being provided with grooves near their axial ends for reducing heat transfer near said ends.

5. The arrangement as in claim 1, the rolls being provided over its surface with material of different thermal conductivity, the conductivity being lower near the axial ends of the rolls than in the central portion thereof.

6. The arrangement as in claim 1, the rolls included in the third means provided with a sprayed-0n metallic layer near the axial ends thereof.

7. The arrangement as in claim 1, the rolls included in the third means provided with an oxide ceramic layer near the axial ends thereof.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,642,057 Dar-ed February 15. 1912 Inventor(g) Erwin Scheufele It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, [73] "Vahrenwalder Strasse" should read Hannover Signedand sealed this 20th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK 'Attesting Officer Commissioner of Patents FORM PO-105O (10-69) co 50375-p59 a u.s4 GOVERNMENT FRlNTlNG OFFICE: (969 0-366-334, 

1. Arrangement for cooling a continuous casting string having elongated rectangular cross section and being guided within a particular guiding frame underneath a casting mold, the combination comprising: first means arranged directly underneath the casting mold to establish a spray water zone for cooling the string by spraying water upon its surface; second means disposed behind the spray water zone in direction of the casting withdrawal path to remove spray water from the casting string; and third means including a plurality of rolls in contact with the broad sides of the string arranged behind the second means in direction of casting withdrawal, said rolls including heat transfer means for extracting more heat from the axial center of the rolls than from the ends.
 2. Arrangement as in claim 1, the second means including at least one roll having smooth walls engaging the casting string over its entire width.
 3. The arrangement as in claim 1, the rolls included in the third means being internally cooled and having internal cooling channels, the radial distance of the channels from the cylindrical surface of the roll being larger at the axial cylinder ends than near the central portion of the rolls.
 4. The arrangement as in claim 1, the rolls included in the third means being provided with grooves near their axial ends for reducing heat transfer near said ends.
 5. The arrangement as in claim 1, the rolls being provided over its surface with material of different thermal conductivity, the conductivity being lower near the axial ends of the rolls than in the central portion thereof.
 6. The arrangement as in claim 1, the rolls included in the third means provided with a sprayed-on metallic layer near the axial ends thereof.
 7. The arrangement as in claim 1, the rolls included in the third means provided with an oxide ceramic layer near the axial ends thereof. 